Radio bomb release system



D. BLITZ RADIO BOMB RELEASE SYSTEM April 5, 1949.V

Filed oct. 18. 1946 2 Sheets-Sheet 1 Q. n nfl va l N z mw L ku AN L? HTLw n L bk la A7 rom/Y I April 5, 1949. D. BLITZ 2,466,531

I RADIO BOMB RELEASE SYSTEM Filed oct. 18. 1946 2 sheets-sheet 2 vATTUP/VY framed Apr. s, i949 .UNITED STATES. vmiTENT omer.

Daniel aslio Radio Corporation of America, a corporation of Wale ynem-Appueauon october 13,1946, serial 16.104.244

4 claims. (ci. 34a- 7) This invention lrelates to radio bomb releasesystems, and more particularly to improvements in systems of the typewhich-transmita signal from the bombing craft to a selected. target.receive the signal after reilection by the targ'et, and compare thetransmitted and' received signals to determine the instant at which abomb should be released to hit the target. One such system, usingfrequency modulated signals, is described in copending U. S. patentapplication Serial No. 524,794, filed March 2, 1944, by Royden C'.Sanders, Jr., and William R. Mercer, nowv Patent No. 2,412,632, issuedDecember 17, 1946, and en-`v titled Radio bomb release system.

Owing to occasional transmission over multiple paths, caused byreflection from the sea or terrain lying between the bomber and itstarget, the signal received at the bombing craft will fade, disappearingand returning at intervals as the target is approached. When the signaldisappears, the effect is similar to that of a remote target, and' thecomputer circuit tends to adjust itself accordingly. Upon reappearanceof the signal, a certain amount of time is required for the computer toreadjust to the true conditions. If this occurs just prior to the properinstant of release, no bomb will be dropped until the signal reappears,and the computer reaches its proper a minimum of additional circuits andcomponents, avoiding any substantial increase in weight landcomplication of the equipment.

The invention will be described with reference to the accompanyingdrawing. wherein:

Figure 1 is a schematic diagram of a bomb release, system embodying thepresent invention,

Figure 2 is a graph showing the variations in frequency of the signalstransmitted and received in the operation of the system of Figure 1,

Figure 3 isa graph showingthe variations in frequency, of 'a beat signalproduced in the operation of 'thesystem of Figurel,

Figure 4 is ra graph showingv typical variation, as a targetisapproached. of a control voltage produced in the operation of the systemof Figure 1,7and

Figure 5 is a graph illustrating ideal variations of said controlvoltage at high and low speeds of the bomber craft, and a compromisebetween said extremes.

Refer to Figurel 1, which illustrates a system like that disclosed inthe aforementioned copend ing Sanders application. A radio transmitterl. `provided with an antenna 3, is connected to a frequency modulator 5.The modulator 5 may be of the vibratory variable capacitor typedescribed in patent application Serial No. 471,003, filed January 1,1943, by Sydney V. Perry and entitled Capacity modulator unit. A squareWave generator 'l excites the modulator 5 through a wave I3. Thetransmitter l is also coupled to the detector i3 througha transmissionline l5. The output vof the detector I3 is applied to an amplilier Il,and thence through an `amplitude limiter i9 to a differential countercircuit 2l. The counter circuit 2| is of the type described in saidSanders application Serial No.v 524,794, now Patent No. 2,412,632,issued December 17, 1946, comprising two averaging cycle countersprovided with a common load resistor 23, arranged so that one provides acurrent flowing upward in the resistor 23 and the other provides acurrent flowing downward in the resistor 23. The counter 2| iselectronicallyv switched by square wave voltage from the generator l, sothat current flows down in the resistor 23 whenA the frequency of thetransmitter i is increasing, and up when the vtransmitted frequency isdecreasing.y

switch 28 is included between the relay 21 and the release mechanism.The relay circuit 21 is designed .to actuate the release when thevoltage of its input decreases to a predetermined value. One such relaycircuit, using a cathodeinput amplifier, is described in'theabove-mentioned Sanders application.

In the system of said Sanders application, the counter output is applieddirectly to the relay circuit. The present system diifers therefrom inthat a so-called memory circuit is provided between the counter and therelay. A capacitor 29 is connected across the input terminals of therelay 27. The upper terminal of the capacitor 29, together with thecorresponding input terminal of the relay, is connected through a diode3| to the counter load resistor 23. The diode 3l is arranged to allowconduction only from the capacitor 29 to the resistor23. A low pass ltercomprising a resistor 33 and a capacitor 35 may be included between theresistor 23 and the diode 3l.

A resistor 31 is connected at one end to the upper terminal of thecapacitor 29. The other end' of the resistor 31 goes to two switches, 33and 4I. The switch 39, when closed, connects the resistor 30 to the tapon the voltage divider 25. 'I'he switch 3l, when closed, connects theresistor 39 to the positive end of the divider 25, which is at apotential in excess of that at which the relay 21 operates.

The switch 5I is ganged with the arming switch 28 so that when theswitch 2B is open, the switch Ill is closed, and vice versa. The switch39 is arranged to be held open normally by an electromagnet 43, and toclose when the magnet 43 is deenergized. The coil of the magnet 43 iscon nected to the output of a rectifier 45, which is supplied from theoutput of the amplier I'I.

The operation of the described system is as follows:

The transmitter I Aprovides a frequency modulated signal which isradiated by the antenna 3. Some of the radiated energy strikes thetarget and is reected back to the antenna I I and applied to thedetector I3, where it is mixed with transmitter output reaching thedetector through the line I5.

Referring to Figure 2.- the frequency of the transmitter output variesas shown by the solid line L The frequency of the signal received at theantenna I varies-as shown by the dash line 203. The variations in thereceived signal are delayed with respect to those of the transmittedsignal by a time Td, which is the period required for radiation totravel from the antenna 3 to the target and back to the antenna I I, andhence is proportional to the distance, d. In addition (assuming thebomber is going towardthe target) the frequency of the received signalis shifted upward owing to doppler effect. This upward shift fs isproportional to the speed of approach s of the bomber to the target.

The output of the detector I3 includes a beat signal whose frequency fbis the difference in frequency of the transmitter output and thereceived signal. The beat frequency fb is lower during upsweep, orincrease of transmitter frequency, than it is during downsweep, ordecrease of transmitter frequency. Thedifference between the upper andlower values of fb is proportional to the speed s. The average value offb is proportional to the distance d.

The beat output of the detector I3 is amplified by the amplifier I1,then limited toa constant amplitude by the limiter I9 and applied to thedifferential counter 2 I. The counter 2l provides; during upsweep. acurrent iu in the resistor 23, proportional to the lower value of thebeat frequency jb. During downsweep, the counter 2l produces a currentid in the opposite direction to the current i and proportional to theupper value of the beat frequency fb.

iu=kl (ad-bv) and id=ka(ad+bv) where a and b are constants determined inthe design of the system, and k1 and k2 are the sensitivities of thecounter circuit when operating positive and negative respectively. Theaverage current in the resistor 23 (ilowing downward) is a= (k1-k2)ld-(k1+k2) bv and the resulting voltage drop (positive at the upper endof the resistor 23) is` The total potential at the upper end of theresistor 23, referred to ground, is

As the bomber approaches the target, Ec decreases because d isdecreasing. The bias voltage E1 and the constants a. b, Ici and k2 aredetermined with respect to each other in advance, making due allowancefor the altitude H at which the bombing run is to be made, so that Ecbecomes equal to the voltage ED at which the relay is set to operatewhen was where g is the acceleration of gravity, 32.2 feet per secondper second.

.The quantity is referred to hereinafter as the time from target, and isdefined as the time which will be required under present conditions forthe bomber to reach a point directly over the target. The quantity isthe time of fall, i. e. the time required for a bomb released at analtitude H to reach the ground. If release is effected when the timefrom target equals the time of fall, the bomb will strike the target.

Owing to the fact that the radio equipment measures the slant speed andslant distance rather than the horizontal components of speed anddistance, the equipment must be adjusted so that E1 follows anapproximation rather than the true relation between speed and distance.This is described in detail in the above-mentioned Sanders application.It is suiiicient for the purpose of the present description to note thatEe decreases with decreasing time from target, and becomes equal toEDwhen the time from target is equal to the time of fall.

Now suppose that as the bomber approaches the target, the receivedsignal fades out. The control Voltage Ec, which has been decreasing in asubstantially continuous manner (see Figure 4) immediately starts up toa maximum value corresponding to that which appears normally when thetargetlE is remote. This results from-thermal c noise in the detector II, which causes the counter age bearing a predetermined relationship tothe time from target, relay means responsive to decrease of inputvoltage to a predetermined value to effect bombrelease, a storage deviceconnected across the input terminals of said relay means,

means for initially charging said storage device d and o. However, thecontrol voltage Ec does not return immediately to the proper value,because the filter capacitor 26 must be discharged down to Ec. Asillustrated in Figure 4, this may not occur until after the time fromtarget has decreased to less than the time of fall, and in the.

above-described Sanders system release will take place too late, or notat all, depending upon whether or not Ec gets down to ED before thebomber passes over the target and loses the signal entirely.

In `the operation of the instant system, the switches 28 and 4I areinitially in the positions shown in Figure 1. As soon as a usable targetsignal is picked up, the coil t3 is energized to open the switch 39.`The capacitor 29 is then charged, through the switch 4| and the resistor3l, to the full voltage appearing across the voltage divider 25. As thebombing run is started, the arming switch 28 is closed, opening theswitch 4I; The capacitor 29 then discharges through I the diode 3|'A andthe resistor 23 until the voltage across it is equal to the voltage Ec.

As Ec decreases in the manner shown in Figure 4, the capacitor 29continues to discharge through the diode 3l to equalize its voltage withEc. When the received signal fades, and Ecincreases, the diode 3lblocks, since it cannot conduct toward the capacitor 29. The switch 39closes and the capacitor 29 continues to discharge through the resistor31. The resistor 3l and the capacitor 29 are so proportioned that thisdischarge occurs at a rate approximating the normal decrease of Ec,which is indicated by the dash line 493 in Figure 4.

If the signal returnsl before the bomber reaches the release point, themagnet 43 reopens the switch 39 and the capacitor 29 starts to dischargethrough the diode as soon as Ec falls belowthe Voltage then existingacross the capacitor 29. Thus if Ec returns to its correct value beforethe time from target becomes equal to the time of fall, the relay iscontrolled by current information, since the voltage applied thereto iskept equal to Ec. If Ec does not return to its proper value in time,release takes place anyway as soon as the capacitor 29 has dischargedsuiliciently through the resistor 31. y

Referring to Figure 5, the curve 50| represents the variation of Ec withtime when the bomber is approaching the target at a relatively highspeed, and the curve 503 shows how Ec varies when the bomber approachesat a relatively low speed. The resistor 3l and capacitor 29k areprocraft, means transmitting a signal to a selected target and means forreceiving said signal after reflection by said target to provide acontrol voltto a predetermined terminal voltage in excess of that whicheffects release, means normally discharging said storagedevice to aterminal voltage equal to said control voltage, a further dischargepath, and means responsive to failure of said received signal to connectsaid further discharge path across said storage device to discharge saidstorage device at a rate approximating the normal rate of decrease ofsaid control voltage.

2. A bomb release system including, on a mobile craft, meanstransmitting a signal to a selected target and means for receiving saidsignal after reflection by said target to provide a control voltagebearing a predetermined relationship to the time from target, relaymeans responsive to decrease of input voltage tc a predetermined value vto eiect bomb release, a capacitor connected across the input terminalsof said relay means, means for initially charging said capacitor to apredetermined voltage in excess of that which eiects release, adischarge pathincluding a unilateral conductor connected to saidcapacitor and meansv to apply said control voltage to said dischargepath to normally prevent discharge of said age, a resistor, and meansresponsive to failure of said received signal to connect said resistoracross said capacitor to discharge said capacitor at a rateapproximating the normal rate of de crease of said control voltage.

3. In a bomb release system including on a mobile craft meanstransmitting a signal to a selected target, means for receiving saidsignal after reflection by said target, computer means responsive tosaid transmitted and received signals to provide a control voltagebearing a predetermined relationship to the time from target, and relaymeans responsive to decrease of input voltage to a predetermined valueto effect bomb release, a system for compensating the effects of fadingor failure of said received signal including a capacitor connectedacross the input terminals of said relay means, means for initiallycharging said capacitor to a predetermined voltage in excess of thatwhich effects release, a unilateral conductor connected between saidcomputer means /and said capacitor to 'prevent conduction from resistoracross' said capacitor to dischargel said capacitor at a rateapproximating the normal rate of decrease of said control voltage.

4. In a bomb release system including on a mobile craft meanstransmitting a signal to a selected target, means for receiving saidsignal after reflection by said target, computer means responsive tosaid transmitted and received signals to provide a control voltagebearing a predetermined relationship to the time from target, and relaymeans responsive to decrease of input voltage to a predetermined valueto eiect bomb release, a system for compensating the effects of fadingor failure of said received signal including a capacitor connectedacross the input ter.- minals of said relay means, a direct currentsource of predetermined voltage in excess of that which emessi eiectsrelease, an arming devicelncludmg means for initially connecting saidcapacitor to'l said source and, upon'arming,r to disconnectlt from saidsource, a unilateral rconductor connected between said computer meansand said capacitor `to preventv conduction fromv said computer meansreceived signal to connect said resistor 1: said capacitor to dischargesaid capacitor at a f rateapproximating the no1-mai rate of of saidcontrol voltage.

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'Emmons crrnn Y `The following references arey of record inthe n f fnient thispatent:y

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